The left ventricle (LV) can dilate considerably in response to volume overload, but may develop systolic dysfunction when dilatation is severe. Echocardiographic enalysis of 80 patients with aortic regurgitation (AR) was performed. In patients with LV end-diastolic dimension (LVDD) less than 70mm, corresponding to a 50% increase in dimension and a three fold increase in estimated LV volume, LV end-systolic dimension (LVSD) increased proportionately and maintained normal systolic function as measured by % fractional shortening (%FS). Above this level of LVDD 1) LVSD increased disproportionately more than LVDD, leading to diminished %FS; 2) %FS decreased in a linear response to increased LVSD. Thus, when diastolic diameter increases by more than 50%, the ability of the LV to maintain normal systolic function is exceeded and progressive dysfunction ensues.